Texas Instruments AN-1870 LM26420 User Manual

1 Introduction
The LM26420 evaluation board was designed to provide two 2A outputs, V
either the HTSSOP package option of the LM26420 for easier probing or the WQFN version for evaluating
the smaller package. The design emphasizes on the compactness of the LM26420 PCB layout and is
thermally optimized. The total solution size is less than 35mm by 40mm. The board supports the
conversion from an input voltage ranging from 3V to 5.5V down to output voltages of 0.8V for each
channel. V and V
OUT1
support output voltages as low as 0.8V or as high at 4.5V, assuming V
EN pins are pulled up to V
logic.
The board's specifications are:
• Input Voltage: 3V to 5.5V
• Output Voltages: 1.2V
• Maximum load current: 2A/output
• Minimum load current: 0A
• Size: 1.35 in. × 1.6 in.
• Peak Current Limit: ≊ 3.2A at 25°C
• Nominal Switching Frequency: 550 kHz or 2.2MHz
2 Powering Up the Board
Since the EN pins are directly tied to the input voltage via jumpers J
simple as connecting a voltage supply from 3V to 5.5V between the V
be 1.2V on V and 2.5V on V
OUT1
care should be taken in powering up the supplies such that the input voltage, V
Absolute Maximum Rating of 7V. If the part experiences voltages greater than 7V for a prolonged period
of time, then damage to the part can occur and then the evaluation board may cease working.
The linear soft-start ramps for the two output voltages and should last about 600 µs. Load can be applied
prior to power-up. If an output is shorted either before or after start-up, removal of the short-circuit
condition should bring the corresponding output back to normal voltage.
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SNVA353B – February 2009 – Revised April 2013
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AN-1870 LM26420 Evaluation Board
are set to 1.2V and 2.5V respectively. The feedback resistor can be changed to
OUT2
by jumpers for easy evaluation but can also be easily controlled by external
IN
and 2.5V
OUT1 OUT2
, assuming the jumpers connect V
OUT2
Copyright © 2009–2013, Texas Instruments Incorporated
SNVA353B – February 2009 – Revised April 2013
and V
OUT1 OUT2
is high enough to support it. The
IN
and J , starting up the board is as
1 2
and GND terminals. There should
IN
to EN for each channel. Great
IN
, does not exceed the
IN
AN-1870 LM26420 Evaluation Board
User's Guide
. It is available in
1